Prosthesis Loosening / Aseptic Prosthesis Loosening - Instability & Loosening of the Joint Replacement

Depending on the cause of prosthesis loosening, medical professionals generally distinguish between two types:

1. Septic prosthesis loosening is caused by an infection in the area around the implant. This is why it is called “septic”—meaning it involves pathogens.
2. Bacterial colonization of the implant is one of the serious complications of joint replacement surgery.

All cases of endoprosthesis loosening in which no pathogens are involved (aseptic) are accordingly classified as aseptic prosthesis loosening. The risk of loosening also depends on the type of prosthesis, its position within the bone, and the length of time since the prosthesis was implanted. Older implants in joints subjected to heavy loads are particularly prone to this condition.

The first symptoms of a loosened endoprosthesis are often pain in the area of the endoprosthesis during weight-bearing activities. As loosening progresses, pain may occur even at rest.

Fractures at or near the implantation site, as well as misalignment and dislocation of the artificial joint, can result from endoprosthesis loosening.

In the event of an acute bacterial infection of the implant, the following symptoms may occur:

• Redness
• Swelling and
• Warmth

These symptoms occur in the area of the implant, accompanied by pain and impaired joint function. Patients often develop chills and fever. Occasionally, the incision site may open and pus may drain from it.

Causes of septic prosthesis loosening

Despite careful joint replacement surgery, bacteria can occasionally (in one to two percent of cases) be introduced into the body.

Normally, the body’s immune system can destroy small amounts of bacteria. However, when a foreign object such as a prosthesis is present in the body, the immune system’s ability to defend itself is weakened.

The bacteria can then multiply more easily and form a type of biofilm. This biofilm fills the space between the bone and the implant. As a result, the prosthesis cannot integrate properly into the bone and becomes loose.

There are several factors that increase the risk of bacterial colonization and, consequently, of septic prosthesis loosening, such as:

• Pre-existing conditions: immunodeficiencies, diabetes mellitus, rheumatoid arthritis, chronic inflammatory skin diseases such as psoriasis, malignant tumors, and coagulation disorders
• Medication therapy with corticosteroids (cortisone) or anticoagulants
• Personal factors such as advanced age, severe obesity, and nicotine, alcohol, and drug abuse

Causes of aseptic prosthesis loosening

The material of the prosthesis and its position within the bone are critical factors. Mechanical wear at the interface between the prosthesis and the bone can trigger an inflammatory reaction, which leads to loosening over time.

This leads to wear and loosening. The abrasive particles trigger an inflammatory reaction. Ultimately, this causes bone resorption, which in turn leads to prosthesis loosening.

Bone cement fractures, cracks, and material spalling are also responsible for implant loosening.

Furthermore, the following factors also play a role in determining whether and when the prosthesis becomes loose, such as:

• primary stability at the time of prosthesis implantation
• surgical experience and quality
• surgical technique, as well as
• the design and material of the implant

Patient-related risk factors for aseptic prosthesis loosening include, for example:

• Advanced age
• Weight
• Accident, fall
• Pre-existing bone damage (osteoporosis, osteonecrosis)
• Pre-existing conditions (axial misalignment, diabetes, etc.)

In the first two years after implantation, periprosthetic infection is a more common cause of revision than aseptic loosening.

Early signs of prosthesis loosening include, among others:

• Nature of the symptoms
• Additional symptoms
• Timing of the joint replacement surgery
• Pre-existing conditions and
• any traumatic events

If a loose prosthesis is suspected, an X-ray of the affected joint region is taken. If possible, doctors compare it with the X-rays taken at the time of implantation.

If necessary, further imaging tests may be required, such as:

• sonography (ultrasound),
• MRI (magnetic resonance imaging)
• CT (computed tomography), or
• scintigraphy (imaging using radioactively labeled substances)

These tests confirm the diagnosis and help clarify specific issues.

If a septic cause is suspected, a blood test is necessary. During this test, doctors have the inflammation markers measured.

An examination of the joint fluid, including testing for bacteria, may also be required.

Specialists in prosthetic loosening are orthopedic surgeons and trauma surgeons with extensive experience in endoprosthetics.

If a joint replacement has loosened, doctors must first remove the prosthesis (explantation). They then implant a new revision prosthesis.

In cases of aseptic prosthesis loosening, explantation and reimplantation are typically performed during a single surgical procedure. This procedure is also known as a one-stage replacement surgery.

The treatment of septic prosthesis loosening is significantly more complex. In uncomplicated cases—which are rather the exception—a single-stage replacement surgery may also be performed.

In this procedure, doctors remove the implant and the infected tissue in a single session. They expand the implant site, clean it, and insert a new prosthesis.

In most cases, however, a two-stage revision surgery is necessary. First, doctors remove the loosened prosthesis, along with all foreign materials and the infected tissue.

They then administer antibiotic-containing material over several weeks in certain joints (knee and ankle).

This serves both to treat the infection and to stabilize the bone. In addition, intravenous and oral antibiotic therapy is administered over several weeks.

Only once the doctors have successfully treated the infection can they implant the new prosthesis.

In cases of aseptic prosthesis loosening, although the prosthesis replacement surgery is complex, it is generally possible without complications thanks to modern implants and materials.

The course and prognosis of septic prosthesis loosening are far more difficult to predict due to the nature of the infection.

The key factors are whether doctors have brought the infection fully under control and whether the revision prosthesis remains free of infection.

Another revision surgery may be necessary, following the steps described above for treating the infection. Under certain circumstances, however, it may also be advisable to fuse the joint.

If the infection cannot be brought under control and continues to spread, amputation is necessary.

Patients can only prevent prosthesis loosening to a limited extent, as most causes are beyond the patient’s control.

It is important for severely overweight patients to lose weight after implantation to reduce the strain on the joint.

Patients should consult with their doctor to determine whether they may engage in sports and activities that put strain on the joints.

They should avoid excessive alcohol and nicotine consumption and should completely abstain from drugs.